The invention relates to hubs and other types of rotary elements, especially to improvements in elements which can be used as hubs of clutch discs in friction clutches for motor vehicles. More particularly, the invention relates to improvements in composite structural elements wherein an annular component is held in a selected axial position on a male component as a result of deformation of a portion of the male component.
French Pat. No. 1,096,443 discloses a two-piece hub for use in the clutch disc of a friction clutch. The male component of the hub is a sleeve which extends through the central opening of a female component constituting a flange wherein the opening is surrounded by a surface having axially parallel teeth that penetrate into the material at the periphery of the sleeve so as to remove shavings and to form in the peripheral surface tooth spaces flanked by surfaces which cooperate with the teeth to transmit torque from the flange to the sleeve when the clutch disc is in use. Prior to slipping the flange onto the sleeve, the diameter of the peripheral surface of the sleeve matches the diameter of the root circle of the annulus of teeth on the flange. The hardness of teeth exceeds the hardness of the material along the peripheral surface of the sleeve so that the teeth act not unlike material removing tools and cut their way into the material of the sleeve as a result of penetration of the sleeve into and through the flange. The sleeve has an external shoulder which acts as an abutment and determines the final axial position of the flange which is thereupon fixed in such position as a result of upsetting of a portion of the material of the sleeve at that axial end of the flange which is remote from the shoulder. A washer is disposed between the flange and the upset portion of the sleeve.
The just described hub is expensive because the internal teeth of the flange must be machined with a high degree of precision so that their root diameter matches the diameter of the peripheral surface of the sleeve. Accurate machining of internal teeth is necessary on the additional ground that this ensures predictable removal of shavings from the periphery of the sleeve during axial movement of the flange toward the shoulder of the sleeve. The diameter of the peripheral surface of the sleeve should not exceed the root diameter of the annulus of internal teeth in the flange because this would entail the development of pronounced radial stresses between the flanges and the sleeve, i.e., the sleeve would tend to expand the flange radially. The peripheral surface of the sleeve also requires a rather expensive treatment. Still further, the shoulder of the sleeve must be provided with a chamber for reception of shavings which are removed from the periphery of the sleeve during axial advancement of the flange toward the shoulder.
A further drawback of the patented hub is that some material of the sleeve penetrates into the adjacent end portions of tooth spaces between the internal teeth of the flange during upsetting of a portion of the sleeve in order to fix the flange in the selected axial position (in which the flange abuts against the shoulder). That material of the upset portion which has penetrated into the tooth spaces tends to expand the flange, and the thus generated forces are superimposed upon the forces which develop as a result of axial movement of the flange toward the stop and concomitant penetration of some material of the sleeve into the aforementioned tooth spaces. The material in the tooth spaces forms a plurality of wedges which apply to the teeth radial stresses and thereby prevent the teeth from transmitting a substantial torque. Furthermore, and unless the peripheral surface of the sleeve and the teeth of the flange are machined with a very high degree of precision, a combination of tolerances in the finish of the peripheral surface and in the finish of internal teeth can entail the development of hairline cracks in the regions of internal teeth while the flange is forcibly advanced toward the external shoulder of the sleeve. Such cracks must be detected and the corresponding hubs must be discarded in order not the affect the reliability of the clutch disc. It must be borne in mind that the flange of the hub in the clutch disc of a friction clutch is formed with several windows for customary coil springs which oppose limited angular movement of the hub with reference to the customary disc-shaped carrier of friction linings. Since the friction clutch should occupy a small amount of space in a motor vehicle, the clutch disc is normally a relatively small constituent of the clutch so that the windows of the flange are placed close to the periphery of the sleeve. In other words, the webs between the windows and the internal teeth of the flange (as measured radially of the clutch disc) are relatively narrow so that the development of cracks in the region of the teeth (as a result of penetration of material into the tooth spaces) unduly weakens the flange and necessitates discarding of the assembled hub.